This invention relates generally to sense amplifiers and more particularly, it relates to a sense amplifier for detecting a small current differential from a semiconductor memory cell array.
Sense amplifiers are generally well known in the prior art and are typically used in electronic circuits to read data out of a semiconductor memory such as an EPROM or EEPROM cell array, a SRAM and the like. These prior art sense amplifiers are used to detect voltage differentials on bit lines which have had a memory array connected thereto. The voltage changes on the bit lines caused by the connection of a memory array thereto are very small and the sensing of such small voltage changes has created a difficult task for memory circuit designers. In addition, unless high tolerances are maintained during the fabrication of the integrated circuit there may be caused unbalanced bit lines which could interfere with the reading of data from a memory array. In order to overcome these problems, it has been provided heretofore the use of a dummy cell array with its own sense amplifier for each of the bit lines. However, the use of a dummy cell array and its associated circuitry tend to increase the size and complexity of the integrated circuit.
In view of this situation, there has arisen the need of a sense amplifier for detecting a small current differential between a selected memory cell and a reference cell in a semiconductor array without requiring a separate sense amplifier for the dummy cell array. In the present invention, the sense amplifier relies upon the use of a FET current mirror arrangement which has inherent design characteristics in integrated circuits. It is commonly known that FET devices which are dimensionally similar, positioned close in proximity to each other on a semiconductor chip, and subjected to a common fabrication process would generally have very similar functional characteristics. This allows the memory circuit designers to avoid the critical dimensional and process tolerances associated with fabricating integrating circuit devices used to detect small voltage differentials.